Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Figure 9 is also available online as a YouTube video clip at: https://youtu.be/3oYv21jcAj4. The figure plates are from frames 16 minutes apart. All images captured with 0.5 s exposure time and are at 40× magnification.
